The steering system is in particular provided for a multi-directional transport vehicle which is used to transport goods, in particular in factory halls or on factory premises. Such steering system can comprise devices for picking up and setting down the goods. These devices can be a transport fork disposed on a mast so as to be raisable and lowerable, or a device that is adapted to the goods to be transported.
To be able to use these transport vehicles, in particular in factory halls where comparatively little space is generally available, the transport vehicles are designed as multi-directional vehicles in which all of the at least two, for example, three, four or even more wheel sets are steered, and at least one of the wheel sets is also rotationally driven.
The individual wheel sets can be composed of a single wheel, or also of multiple wheels, for example, arranged in pairs, wherein the latter is in particular advantageous when the transport vehicle is to be used for relatively heavy loads.
In order to coordinate the steering angles of the steered wheel sets, these multi-directional transport vehicles routinely comprise a steering system which can, for example, comprise the below listed steering programs from which the operator can select both when traveling longitudinally and when traveling transversely offset therefrom by an angle of 90°:                Positioning all wheels in the longitudinal or transverse direction, i.e., the transport vehicle moves straight ahead in the longitudinal or transverse direction.        All-wheel steering, i.e., all steered wheels are steered by a steering element when the steering is actuated so that a correct steering geometry is obtained. This has the result that the rotational axes of all wheels intersect in one point, which is known as the steering point or center of steering.        Diagonal steering, i.e., during a steering process, the wheels are steered out of the longitudinal or transverse direction thereof in the same direction of rotation so that the center of steering (as with pure longitudinal or transverse traveling) is at infinity.        Front or rear axle steering, i.e., the wheels disposed at the front or rear are steered relative to the particular direction of movement, for example, relative to the center of steering.        
The steering system can also include special steering programs, such as for a carousel model, wherein the wheels are steered so that the vehicle rotates in a circle about a vertical axis, or for parking, where the rotational axes of at least some of the wheels are oriented perpendicularly to one another for the purpose of preventing the vehicle from rolling away.
It is possible to switch between the individual steering programs during travel. The driver therefore does not need to stop the transport vehicle, for example, when leaving a long goods aisle, where the vehicle is usually operated with the wheels oriented in a straight-ahead position, in order to switch to all-wheel steering, for example, which entails significant time savings.
The disadvantage in the steering system described in DE 201 17 198 U1 is that the switch of the steering program during travel can result in relatively abrupt directional changes which are quite difficult for an operator to control.
A steering system for a transport vehicle is described in EP 1 657 140 B1 which can be steered independently of specific steering programs so that is as variable as possible and therefore maneuver-friendly.
The above steering system therefore comprises a first further operating element for continuously displacing the steering line, and a further second operating element for continuously steering the principal direction of the vehicle, in addition to the steering setpoint generator (such as a steering wheel). A steering system is thereby to be created with which an intuitive steering is provided to increase flexibility of the steering system.
The disadvantage of the above steering system is, however, that the total of three steering setpoint generators require significant practice by the operating staff in order to steer a vehicle configured with this steering system with sufficient precision.